Lashkar-e-Tayiba terrorist Zaki-ur Rehman Lakhwi, accused of masterminding the Mumbai attacks, is among over 20 members of the group arrested by Pakistani security forces during a crackdown in Pakistan occupied Kashmir.

The security forces, including the army, on Sunday launched a crackdown on the Lashkar and its front organisation, the Jamaat-ud-Dawah, in PoK and other parts of Pakistan. Helicopters were used in the operation in Muzaffarabad, the capital of PoK.

Ajmal Amir Iman Qasab, the lone terrorist captured in Mumbai after the attacks, had named Lakhwi as one of the Lashkar men who had planned the strike.

Lakhwi was among more than the 20 Lashkar members arrested in Muzaffarabad during a major army operation on a camp used by the outlawed group, the Dawn newspaper, quoted sources, as saying.

There was no immediate official word on the crackdown.

The Dawn said there were reports that similar actions were planned in some cities and towns of Punjab, a province where the Lashkar and the Jamaat have a significant presence.

Qasab, the terrorist captured in Mumbai, hails from a village in Okara district in Pakistan's Punjab province.

Pakistan is under intense international pressure, including from the US, to take action against the Lashkar for its involvement in the Mumbai attacks. The Lashkar was founded by Hafiz Mohammad Saeed who formed the Jamaat soon after the Lashkar was banned in Pakistan in 2001.

Local residents said they had seen army personnel taking control of an area along Shawai Nullah, five kilometres northwest of Muzaffarabad, where the Lashkar possesses a large camp with several buildings.

The troops sealed off the area after they launched their operation.

"I saw an army helicopter hovering over the area and around 5 pm I heard two or three loud explosions," a woman who lives in the area told Dawn. Another person said the helicopter might have been used to airlift people detained or injured during the operation.

There were also unconfirmed reports of an exchange of fire. Ambulances from hospitals in Muzaffarabad were called to the area by troops, but witnesses said they returned without anyone inside.

In Chehla Bandi area in PoK, soldiers checked vehicles bound for the Neelum valley.

In May, the United States Treasury department had frozen the assets of four Lashkar terrorists including Mohammad Saeed, its leader; Lakhwi, its chief of operations; Haji Muhammad Ashraf, its chief of finance -- all Pakistanis -- and India-born Mahmoud Mohammad Ahmed Bahaziq, a Lashkar financier.